In the food, pharmaceutical, and cosmetics industries it is advantageous to be able to package relatively fluid substances in individual dispensers. Such dispensers comprise a dispenser valve mounted in a sealed manner on a container containing the substance. The valve conventionally comprises a hollow rod which is pushed down for the purpose of opening the valve and the substance is then delivered along the rod. In order to facilitate this operation, it is conventional to provide a pushbutton which is adapted firstly to engage on the hollow rod of the valve and secondly to provide a purchase for the user of the dispenser. The pushbutton then includes an outlet channel establishing communication between the rod and an orifice in the surface of the pushbutton through which the substance is delivered.
When used with semi-liquid substances such as creams, lotions, and other pastes, such dispensers nevertheless suffer from a problem relating to the outlet channel of the pushbutton. After the dispenser has been actuated for the first time, this channel fills up with the substance. As a result, a certain quantity of substance remains trapped in the channel. After actuation, the substance generally remains therein, in contact with ambient air via the outlet orifice. Depending on the nature of the substance, it may then be degraded, for example the substance may dry out and harden inside the outlet channel, thereby blocking it, or oxidation may denature the volume of substance contained in the channel, or it may become contaminated with bacteria from the surrounding water vapor, thereby rendering all further substance dispensed from the dispenser potentially harmful.
In the prior art, attempts have been made to solve this problem by providing the pushbutton with a valve for closing its outlet orifice. For this purpose, European patent application EP-A-O 129 643 filed in 1984 by Pfeiffer proposes using a needle fixed to two pistons placed inside the outlet channel of the pushbutton. The needle co-operates when at rest with the outlet orifice which then constitutes the seat of the valve. While dispensing is taking place, the pressure delivered by the substance acts via the two pistons to withdraw the needle and thus open the orifice.
This system suffers from the drawback that the part used for obstructing the outlet orifice is difficult to manufacture. The two pistons it includes must be provided with sealing rings ensuring sealed contact with the inside wall of the outlet channel. However the diameter of the outlet channel is generally very small (a few millimeters). The molding of such fine lips so fine is so expensive that the cost of the pushbutton is no longer compatible with its purpose.
An object of the present invention is thus to provide a cheaper valve for the outlet channel of a pushbutton for dispensing semi-liquid substances.